Stabilization of polyesters

ABSTRACT

Polyesters, especially beta-lactone based polyesters such as polypivalolactone, are stabilized against thermo-oxidative decomposition by admixing therewith phthalimide alone or in combination with N-acyl-p-aminophenol as an antioxidant.

United States Patent 1 Heuser et a1.

[ 51 Apr. 10, 1973 STABILIZATION OF POLYESTERS Inventors: Giinther Heuser, Troisdorf-Oberlar; Norbert Vollkommer, Troisdorf, both of Germany Dynamit Nobel Aktiengesellschaft, Troisdorf, Germany Filed: July 14, 1971 Appl. No.: 162,475

Assignee:

Foreign Application Priority Data July 24, 1970 Germany ..P 20 36 712.8

US. Cl. .....260/4 5.8 A, 260/457 P, 260/459 R,

' Int, Ch; ..C08g 51/60 Field of Search ..260/45.95, 45.8 N, 1 260/459 Primary ExaminerDonald E. Czaja Assistant Examiner-V. Hoke Attorney-Ralph D. Dinklage et a1.

{57] ABSTRACT Polyesters, especially beta-lactone based polyesters such as polypivalolactone, arestabiiized against thermo-oxidative decomposition by admixing therewith phthalimide alone or in combination with N-acyl-paminophenol as an antioxidant.

5 Claims, No Drawings BACKGROUND The invention relates to the stabilization of polyesters against thermo-oxidative decomposition during the fabricating process and against the effects of light and the atmosphere. v

A number of polyesters have high meltingtemperatures. These include polypivololactone and other polyesters which are obtained by the ring-opening polymerization of fi-lactones on the basis of a, a-dialkyl-B-ptopiolactones, as well as polyarylesters and others.

Polypivololactone is characterized by high crystallinit y and great hardness. Consequently, this polyester is of specialinterest as a fiber material and as a thermoplastic. The melting temperature is between 230 and 240 C. Since fabrication is performed as a rule at a temperature above the melting temperature, fabrication temperatures between 250 and 300 C are necessary.

It is knownthat, at these fabrication temperatures,

I the action of air results in a great loss of the molecular weight combined with an impairment of mechanical properties. At 270 C, the molecular weight of polypivololactone drops within minutes from about 150,000 to about 30,000, and on down to 20,000 within another 30 minutes.

The decomposition of polyesters can be retarded by the addition of stabilizers. As a rule, combinations of a stabilizer and an anti-oxidant are used, resulting in a 'synergeticenhancementof their effectiveness. French Patent 1,523,848 and British Patents 1,055,740 and 1,120,920 describe such combinations. The stabilizers used are compounds of varying structure, such as nitroso compounds, e.g. 'riitrosarnines and nitrosophenols, and ai'ylguanidines, and also thio cornpounds, e.g., derivatives ands'alts of dithiocarbamic acid. The antioxidants are phosphitesjespecially tri- (nonylphenyl)-phosphite, amines, especially N-phenylfl-naphthylamine, and phenols,especially sterically inipeded phenols with bulky substituents in the ortho position, such as 2,6-di-tert. butylphenol. However, when these compounds are used in the stated range of concentrations, important disadvantages are encountered.

As a result of the high fabricating temperature, the action of air produces intense discoloration ranging from intense yellow todark brown, depending on the stabilizer or antioxidant usedJ-The sulfur compounds, particularly, result in a brown discoloration. In regard to fabrication into shaped bodies and fibers and the dyeing thereof discoloration isan undesirable factor making the achievement of light shades of color virtually impossible. Furthermore, if the sulfur compounds are'used an unpleasant odor is involved which is troublesome when it comes to technical fabrication. When aromatic amines are used there is also an after darkening of the polyester mass under the effect of light and the atmosphere.

SUMMARY The subject of the invention is'the use of phthalimide for the stabilization of polyesters, alone or in combination with an Nacyl-p-aminophenol as antioxidant, each in quantities of 0.001 to 1 wt. percent, preferably 0.01 to 0.1 wt percent, with respect to the polyesters.

An enhanced synergetic action is achieved by the addition of the antioxidant.

. DESCRIPTION The N-acyl-p-aminophenols (amidophen'ols) used as antioxidants are described by the general formula HO-Q-If-QLJ).

wherein R represents an aliphatic or aromatic,

branched or unbranched hydrocarbon radical. Preferred antioxidants are for example, n-butyryl-p- Y aminophenol, n-pelargonyl-p-amino-phehol, n-lauroylp-aminophenol, n-stearyl-p-aminopheno'l.

The stabilizing effect of phthalimide alone or in combination with N-acyl-p-aminophenols, is achieved with polyesters regardless of the nature and manufacture of the polyesters. For example, polyesters which have been made from dicarboxylic acids such as terephthalic acid and bivalent alcohols such as ethylene glycol, 1,3-

butylene glycol, 1,2-propylene glycol, neopentyl glycol,-

such as alkyl alcohol, or the above-named glycols, and

sometimes other unsaturated compounds such as styrene, cyclopentadiene or dialkylphthalate, can be stabilized, and so can the so-called polyester-urethane elastomers, if necessary.

Stabilization in accordance with the invention is especially valuable for high-melting polyesters, suchv as those of the polylactone group, as for example the polya,a-dialkyl-B-propiolactones and their copolymersand mixtures, especially polypivalolactone, and those of the polyaryl ester group, since hitherto their stabilization has been inadequate for the high fabricating temperatures that are required.

The advantage of stabilization in accordance with the invention over other known stabilizers lies in the greater synergetic effect of the described stabilizer combination, which is reflected by the weight ratio of stabilizer to antioxidant, of 1 0.5 as compared with l 4 and l 2 (see Table). The quantity of the antioxidant can thus be reduced to about one-tenth of what must be used according to the best state of the art.

Discoloration of the polyester compounds both during fabrication and under the influence of light and the atmosphere is completely prevented- Furthermore, there is no foul odor involved in fabrication.

The addition of the stabilizer combination can be performed by mixing the components together in which the polyester itself does not dissolve, and then EXAMPLE removing the solvent by evaporation. The fabrication of the polyester is performed as a rule from the molten Poly-a a-diethyl-fi-propiolactonein powder form, state. with an inherent viscosity of 2.9, is stabilized with 0.06-

Polypivalolactone was used in testing the effective- 5 wt percent of phthalimide and 0.03 wt percent of n-launess of the stabilizer combination, because, due to its royl-p-aminophenol and the polyester is kept in the high fabricating temperature, the stabilizer must satisfy melted state in an open vessel at 260 C for minutes the most exacting requirements. The stabilized and 40 minutes. Within these periods of time the polyester was kept in the fused state at 270 C under viscosity diminished to 2.65 and 2.2, respectively.

air, while the loss of molecular weight was tested with a 10 A specimen of poly-a,a-diethyl-B-propiolactone. of viscosimeter. The measurements were performed at the same viscosity of 2.9 was degraded, under the same C in trifluoro-acetic acid at a concentration of 0.5 conditions as Example 5, but without stabilizer, to an g/100 ml. The inherent viscosity was determined, inherent viscosity of 1.4 and 1.12, respectively.

Anti- 10 min., 40 inin., Stabilizer oxidant Stab. Antiox. 270 C. 270 C. Color after 40 minutes at 270 C.

Example:

1 30,000 20,000 Colorless. 2 A 0. 10 115,000 80,000 Do. 3 A B 0. 05 O. 02 124, 000 105, 000 Do. 4" A C 0. 05 0. 02 124, 000 104, 000 Do. Examples (for purposes of eompariso 1 1 D 0. 10 116. 000 78, 000 Light brown. 2 D 'E 0. 05 0. 20 118, 000 1 4. 000 Light brown; dark brown after-discoloration. 3 F G 0.05 0. 10 .10, 000 62, 000 Orange ycllo\v.

Example 1: Polypivalolactone with no additive. Initial molecular weight 148,000. Stabilizers and Antioxidants: A=Phthalimide; B=n-st0aryl-p;aminophonol; C =n-pelargonyl-p-aminoplicnol; I)=totramethylthiuramidisultide, E=N-phenyl-fl-napthylamiue; F=l-nitroso-2-naphth )l; G=tris-(nouylphenyD-phosphite.

and from this the molecular weights were computed ac- What is claimed is: cording to the equation: 1 inch. 3.10" 'M. l. A polyester composition stabilized against thermo- In the case of poly-a,a-diethyl-B-propiolactone, only oxidative decomposition comprising said polyester and the inherent viscosity is given, for lack of a molecuas the stabilizer, phthalimide and an N-acyl-p-- lar weight equation. aminophenol of the general formula a i o v EXAMPLES 1 to 4 Q'E d in which R re resents an ali hatic or aromatic 1.5 g of polyprvalolactone in powder form (grain size use p 0.1 to 0.5 mm), with a molecular weight of 148,000, is zzzgx; 3 2;21 :353 g gg i g i zi g k zf z wetted with the solution of the stabilizer combination 40 g d th 0] t pe y g in acetone, the solvent is evaporated, and the specimen g 2? 2 5 1 2: Z' 1 wherein the 01 ester s 5 IS dried in vacuo over phosphorus pentoxide. Then the P p y stabilized polyester is kept in the open reaction glass in polymer based aadialkylfi'pmPiolactones or their the following table and compared with effective stabilcopolymers.

3. Composition of claim 1 wherein the polyester is poly-a,a-dimethyl-B-propiolactone.

4. A composition according to claim 1 wherein said N-acyl-p-aminophenol is N-stearyl-p-aminophenol.

5. A composition according to claim 1 wherein said N-acyl-p-aminophenol is N-pelargonyl-p-aminophenol.'

a metal bath at 270 C, and the loss of the molecular weight after cooling of the specimen is determined 5 after 10 and after 40 minutes. The results of the stabilization process of the invention are summarized in izer combinations from the literature (Examples 1 to 3). 

2. Composition of claim 1 wherein the polyester is a polymer based on Alpha , Alpha -dialkyl- Beta -propiolactones or their copolymers.
 3. Composition of claim 1 wherein the polyester is poly- Alpha , Alpha -dimethyl- Beta -propiolactone.
 4. A composition according to claim 1 wherein said N-acyl-p-aminophenol is N-stearyl-p-aminophenol.
 5. A composition according to claim 1 wherein said N-acyl-p-aminophenol is N-pelargonyl-p-aminophenol. 